Traditionally, security concerns have been given a low priority in the building process. Until the late 1960s, when the federal government took an interest in crime prevention in urban housing, few serious attempts were made to develop a workable philosophy for controlling crime through architectural planning and design. In the early 1970s, several studies financed through the Law Enforcement Assistance Administration and the Department of Housing and Urban Development demonstrated that architectural design could be used effectively to influence crime rates in housing developments. These studies showed that by combining security hardware, psychology, and site design, a physical environment could be developed that would, by its very nature, discourage crime.
The CPTED Concept
Crime Prevention Through Environmental Design, or CPTED (pronounced sep-ted), is a relatively new concept. The idea of using the physical environment as protection against attack may to date back to the cavemen. However, it wasn't until recently that the problem of creating a defensive environment was approached from both the physical and the psychological aspects at the same time. This blend of disciplines is the essence of the CPTED concept.
The goal of CPTED is the reduction of opportunities for crime to occur. This reduction is achieved by employing physical design features that discourage crime, while at the same time encouraging legitimate use of the environment.
CPTED also makes possible designs that offer protection without resorting to the prison camp approach to security. Use of fortress-type construction is minimized, and where necessary, integrated into the overall design, reducing negative visual impact. This approach is also cost-effective, since hardware applications are made during construction rather than added at a later date.
To understand fully how CPTED is used, one must examine its components and the philosophy behind them. Although crime prevention through design is itself relatively new, its individual elements are common security techniques. The uniqueness and success of CPTED stems from the manner in which these techniques are integrated with, and applied to, the architectural design process.
To provide maximum control, an environment is first divided into smaller, clearly defined areas or zones. These zones become the focal points for the application of the various CPTED elements. "Defensible space" is the term used to describe an area that has been made a "zone of defense" by the design characteristics that create it.
Under the defensible space guidelines, all areas are designated as either public, semi-private or private. This designation defines the acceptable use of each zone and determines who has a right to occupy it under certain circumstances.
Public Zones. These areas are generally open to anyone and are the least secure of the three zones. This is particularly true when the zone is located within a building or in an area with uncontrolled access and little or no opportunity for close surveillance.
Semi-private Zones. These areas create a buffer between public and private zones and/or serve as common use spaces, such as interior courtyards. They are accessible to the public, but are set off from the public zone. This separation is accomplished with design features that establish definite transitional boundaries between the zones.
Private Zones. These are areas of restricted entry. Access is controlled and limited to specific individuals or groups. A private residence is a good example of a private zone.
Division between zones is generally accomplished with some type of barrier. These can be either physical or symbolic.
Physical barriers, as the name implies, are substantial in nature and physically prevent movement. Fencing, some forms of landscaping, locked doors, and the like are examples of physical barriers.
Symbolic barriers are less tangible. Nearly anything could serve as a symbolic barrier. The only requirement is that it define the boundary between zones. This type of barrier does not prevent physical movement. All that is required is that it leave no doubt that a transition between zones has taken place. Low decorative fences, flower beds, changes in sidewalk patterns or materials, and signs are examples of symbolic barriers.
Territoriality involves an individual's perception of, and relationship with, the environment. A strong sense of territoriality encourages an individual to take control of his or her environment and defend it against attack.
A sense of territoriality is fostered by architecture that allows easy identification of certain areas as the exclusive domain of a particular individual or group. This feeling is enhanced when the area involved is one the individual can relate to with a sense of pride and ownership. It is not enough for a person simply to be able to defend his environment, he must also want to defend it. That "want" results from territorial feelings of pride and ownership.
The term ownership when used in this context does not necessarily mean actual legal ownership. It can be, and very often is, a perceived ownership resulting from an individual's relationship with the environment. Office workers, for instance, may feel a sense of ownership for the office in which they work.
Surveillance is the principal weapon in the protection of a defensible space. Criminals are least likely to act when there is a high risk of their actions being witnessed. Environments in which legitimate occupants can exercise a high degree of visual control increase the likelihood of criminal acts being observed and reported.
Informal Surveillance. Opportunities for informal or natural surveillance occur as a direct result of architectural design. Designs that minimize visual obstacles and eliminate places of concealment for potential assailants offer the most protection against crime. These open designs also encourage use of the environment, as people feel safer when they can easily see and be seen.
The use of defensible space in conjunction with natural surveillance is a potent crime prevention tool. The establishment of transition zones gives both the occupant and the intruder clear and definite points of reference. For the occupant, an intruder's entrance into restricted space creates cause for attention and possible alarm. For the intruder, entering restricted space spotlights his actions, elevates his anxiety level, and greatly increases his risk of being discovered and apprehended.
Formal Surveillance. Formal surveillance methods, such as closed-circuit television, electronic monitoring, fixed guard posts, and organized security patrols, are normally used only when natural surveillance alone cannot sufficiently protect an area. Public and semi-private zones that are concealed from view or that experience regular periods of isolation or inactivity may benefit from some type of formal surveillance.
Elevators, interior corridors, parking lots, public areas of buildings accessible after business hours, and exterior pedestrian pathways are potentially vulnerable locations where the application of formal surveillance methods might be justified.
Good lighting is one of the most effective crime deterrents. When used properly, light discourages criminal activity, enhances natural surveillance opportunities, and reduces fear.
The type and quantity of light required will vary from application to application, but the goal remains the same in all cases. To the degree possible, a constant level of light providing reasonably good visibility should be maintained at night. The absolute level of light, provided it meets minimum standards, is less critical than the evenness of the light. Bright spots and shadows should be avoided. Highly vulnerable areas and those that could conceal a potential attacker should be illuminated more brightly than areas designed for normal activity. The object is to light up the criminal without spotlighting the victim.
As used in CPTED, lighting also plays a part in creating a feeling of territoriality. Lighting can influence an individual's feelings about his environment from an aesthetic as well as a safety standpoint. A bright, cheerful environment is much more pleasing than one that appears dark and lifeless. The ability to feel good about one's environment is important in developing a sense of pride and ownership.
Landscaping design, like architectural design, plays a significant role in CPTED. Landscaping is versatile and can be used to perform a variety of design functions.
As a symbolic barrier, landscaping can mark the transition between zones. Features such as decorative fencing, flower beds, ground cover, and varied patterns in cement work can clearly show separation between zones. If more substantial barriers are needed, shrubbery such as evergreen hedges can be used to create more formidable obstacles.
From a surveillance standpoint, landscaping can be critical. Such factors as growth characteristics of plants and their placement in relation to potentially vulnerable areas are extremely important.
Visual corridors must be maintained in open, park-like areas as well as in densely planted areas. As a rule, visual surveillance corridors can be maintained by limiting shrubbery to a maximum height of three feet and trees to a minimum height of six feet at the lowest branches. This approach ensures that visibility between three and six feet from the ground will always be relatively unimpaired.
Another function of landscaping in crime prevention is aesthetics. Again, an attractive environment generates a sense of pride and ownership.
The problem with the physical security of most building projects lies in the fact that the people designing the systems don't understand crime and criminals and how they work. The unfortunate result of this practice can be seen easily in soaring residential and commercial burglary rates.
Enlightened physical security planning can contribute considerably to the overall success of a project. The proper application of security hardware and the elimination of security weaknesses from a structural standpoint can have a significant impact on future crime problems.
As an element of CPTED, physical security planning is not intended to create an impenetrable fortress. The goal is merely to make penetration more difficult and time-consuming. Degree of difficulty and length of delay are key factors in reducing the probability that crime will occur.
Many of the individual CPTED elements should be familiar to the security professional. Hardware, lighting, and surveillance are all standard tools of the trade. The emphasis of CPTED is not just on the tools, however. It is how the tools are used that makes the difference. Normally, a building is built and then secured. With CPTED, it is secured, then built. More importantly, not just the building is secured but also the space around it. The security program is integrated into the environment, not just added on.
CPTED was originally developed to reduce crime in public housing projects, but its applications are unlimited. It is a concept that can work not only in housing, but in businesses, industries, public buildings, parks and recreation areas, and schools. It is a concept that can be used effectively to secure one building or an entire city.
This is a revision of an article by the same name originally
in the April 1981 edition of Security Management Magazine.